Facebook accounted for more than 31% of all display ad impressions in the US last quarter, according to statistics released this morning by ComScore.

The site delivered 347 million ad impressions -- that's up 17% from Q3 of last year, which is the last time ComScore reported quarterly numbers. Facebook also grew its display market share 8 percentage points since that time, from 23%.

Nobody else is even close -- number-two Yahoo comes in at 10%, and the market drops rapidly from there.

This only measures on-site display advertising, however. Ad networks account for a large portion of display advertising, and there companies like Google, Yahoo, and AOL are ahead of Facebook, as ComScore's monthly stats show. (A PDF of March stats is here -- check out the ComScore Ad Focus rating)